Guillotine dampers are employed where it is necessary for safe entry to be made into duct systems carrying hot gases and corrosive, abrasive and dirty materials.
Such dampers have framework surrounding the flow path, a blade and a bonnet in which the blade is normally housed but movable into a duct-blocking position to establish the closed position of the damper in which margins of the blade extending outside the flow path are sealed to the frame in blade guides. Air under pressure is employed to ensure that there is no leakage of duct gases into the area to be entered.
One of the problems in ensuring that safe entry may be made into such a system is that such frame areas required for sealing tend to collect debris and the use of air to flush debris from such areas is necessary when the damper is open to ensure that such will not be so present as to cause leakage when the damper is closed.